The regulation of cellular proliferation and differentiation is integral to the formation of tissues and structures in all multicellular organisms. The mechanisms and cellular processes that regulate proliferation and fate specification, when aberrant, are intimately tied to oncogenesis and other human diseases making them highly relevant biological issues. Many questions remain unanswered as to the mechanisms whereby progenitor populations are maintained throughout development, how progenitor cells are triggered to exit the cell cycle with spatial and temporal precision and what signals or cues direct them to differentiate as specific cell types. Experiments described in this grant aim to elucidate these processes and will focus on the neural retina. Specifically, the grant has two aims; 1) to characterize the role of Id helix-loop-helix family members, Id2 and Id3, during the proliferation and differentiation events of the zebrafish retina and 2) to identify novel genes and chemicals affecting proliferation and differentiation events in the zebrafish retina.